The present invention relates to optically linked data processing systems, and more particularly, to optical couplers used with optical transmission lines in such data processing systems.
In data processing systems, fiber-optic transmission of data offers many advantages over conventional forms of data transmission. For example, signals carried over fiber-optic cables are generally not affected by electromagnetic or radio frequency interference. Also, fiber-optic cables do not spark or short circuit, and are capable of eliminating ground loop problems by providing electrical isolation between optically connected equipment.
In the past, each optical transmission line in a data processing system generally consisted of a bundle of optical fibers. A single bundle interconnected the various stations within the system and each fiber within the bundle carried the same signal. Optical couplers for connecting stations to bundles of fibers in such systems are known and have been disclosed, for example, in U.S. Pat. No. 4,072,399, issued to R. E. Love, et al.
One problem associated with present and proposed optical transmission lines and couplers is that they are not generally acceptable in a data processing system, such as a multiprocessor system, where it may be desirable for two or more stations to communicate with each other simultaneously. In such a system, the simultaneous transmission of two messages over a single optical transmission line makes it difficult for a station to detect either message. Furthermore, a single optical transmission line for carrying messages in either direction will often experience significant signal losses at couplers and other connection points along the line.
With the advance of fiber-optic technology to the point of making single fiber connections readily available and inexpensive, there has arisen the need for data processing systems having single fiber transmission lines and reliable, yet inexpensive, coupler modules for coupling stations to such transmission lines.